EDSE 732 SECONDARY SCIENCE METHODS
4/17/10
Lesson Plan – Inquiry teach on the application of Ohm’s law
Moritz Huegle
1. Topic of the lesson
Series and parallel electrical circuits – experiments and calculations using Ohm’s law or
“How does a Christmas light set work?”
This lesson will use the everyday example of a light set to introduce series and parallel
electrical circuits. The students derive the relationship between the current, voltage and
resistance in complex circuits with different branches in experiments.
2. Class
The lesson plan is taken from a unit about the concept of the electrical resistance in
physics. It is designed for an eleventh grade physics classroom. The students are
familiar with the basic concepts about electricity and have profound knowledge about the
mathematical techniques such as proportionality and anti-proportionality that will be used
during the lesson.
3. Standards
The students will be measuring current, voltage and resistance in series and parallel
electrical circuits with an analog and digital multimeter in order to record the information.
(Standards P-1.3 and P-4.4)
Working with voltage sources and the components of electrical circuits it is important for
the students to develop an understanding of how to work with electric instruments safely.
(Standard P-1.2)
Organization and interpretation of the collected data using tables, models and formulas
will be important in order to calculate the relationship between the three quantities in the
circuits and different branches using Ohm's law. (Standards P-1.5 and P-4.5)
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EDSE 732 SECONDARY SCIENCE METHODS
4/17/10
Lesson Plan – Inquiry teach on the application of Ohm’s law
Moritz Huegle
4. Objectives
•
Students should be able to indicate the differences between series and parallel
electrical circuits
•
Students should be able to calculate electrical resistances, currents and voltages
in the circuits using Ohm's law.
•
Students should be able to use scientific apparatuses safely.
•
Students should be able to put together different types of electrical circuits.
•
Students should be able to set up, execute experiments and draw schematic
circuit diagrams of complex circuits
•
Students should be able to analyze, evaluate and interpret the data afterwards.
•
Students should be able to present their results on a transparency in class
•
Students should be able to develop further social competences. They see the
importance of individual effort during group work and respect each other’s
results. They also engage actively in classroom discussions.
5. Context
The present unit is about the electrical resistance. Its definition was introduced in the first
lesson: R:=U/I (U is the voltage, I the current and R is the resistance)
The characteristic curves of high- and low-temperature conductors and constantan were
recorded using simple circuits. During the experiments the students learnt how to
measure current, voltage and resistance at certain points in the circuits and have
become familiar with the use of measuring devices such as volt- and ampere-meter.
The second lesson focused on different examples of resistors such as light bulbs and
heating devices. The purpose was to introduce the connection with the everyday life of
the students.
The heat losses of electrical devices and resistors were discussed when looking at the
light bulb. Only 6% of the energy is converted in light whereas 94% of the energy is lost
due to heat. The importance of this subject was outlined talking about the current action
of banning traditional light bulbs by replacing them with energy-efficient light bulbs in
Europe.
The dependencies of the resistance on the material (density ρ), on the length (l) and on
the cross section area (A) have been examined in the third lesson. The students set up
experiments using different wires, varying the length and cross section area. They once
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EDSE 732 SECONDARY SCIENCE METHODS
4/17/10
Lesson Plan – Inquiry teach on the application of Ohm’s law
Moritz Huegle
again measured the voltage and current to calculate the resistance.
The final conclusion the students stated was that the resistance is proportional to ρ*l/A.
Ohm’s law was derived in the previous lesson.
The dependency of the resistance on the temperature was examined leading to the
formulation of Ohm’s law: The quotient of voltage and current defined as the resistance
is constant when the temperature is held constant.
Voltage and current are thus directly proportional. (U=R*I)
So far only simple circuits have been examined. At home students are confronted with
all kinds of resistors and electrical devices such as heating devices, light bulbs and
multimedia devices, which are most likely, used in more complex circuits. After this
lesson students should be able to transfer their knowledge into their everyday life.
This lesson plan is designed to cover complex constructions such as series and parallel
circuits. The students are able to measure one resistor in a circuit and will now work with
possibilities to put more than one resistor in a circuit. Deriving the constant quantities
and the relationships between the quantities in the different circuits.
Saving energy is currently a huge global issue. Scientists come up with new energy
saving ideas everyday. Talking about resistance and transferring the knowledge to
everyday situations is a good way to direct their attention to this subject of global
concern. The second part of the lesson plan is related to this matter as it deals with the
calculation of the quantities in a series of everyday examples such as Christmas
illumination, minimum and maximum number of electrical devices in different circuits and
ways to make light bulbs shine at the same efficacy.
The subject of the last lesson of the unit about resistance will review the basic properties
of series and parallel circuits and will then focus on the discussion of even more complex
circuits such as the Wheatstone bridge, voltage dividers and dimmers.
The students will again be calculating the important quantities using their knowledge
about simple series and parallel circuits to simplify the complex circuits.
This unit will provide the students with a general knowledge about resistances in
electrical circuits. They should be able to apply their scientific knowledge in their
everyday life, explaining the matter to others but also thinking critically about energy
matters. The knowledge provided will enable the students to engage in energy saving
knowing where and why it is useful and sometimes even necessary. They will also be
able to use electrical devices safely knowing about the danger of high currents and the
connection to voltage and resistance.
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EDSE 732 SECONDARY SCIENCE METHODS
4/17/10
Lesson Plan – Inquiry teach on the application of Ohm’s law
Moritz Huegle
6. Materials
Items per class
-
An old light set that turns off if one bulb burns out or is taken out
Items per group
-
Voltage source or a sufficient amount of batteries
-
a few wires or electronic snapkits with light bulb sockets and sockets for the
batteries
-
3-4 light bulbs
-
a volt- and ampere-meter or a multimeter (analog or digital)
-
2 transparencies and pen or 2 big sheets of paper and markers
Items per student
-
Handout with instructions for the experiments and the measurement in the
circuits
-
Worksheet about the relationship and the measurement of current, voltage and
resistance in series and parallel circuits
7. Instructional Sequence
Time
in
Min
Section
Methods
media
Planned process and activities
.
5
Introduction
Teacher (T) shows the light set noting that each
Impulse
light bulb should not be used with more than
20
Stating the
10V. But still we put it in a socket with 110V
problem
“How does that work?”
Instructions
see handout
Light set
Frontal
for the
introductions
experiments
(Handout)
Laboratory
Students (S) try to come up with a hypothesis
Group
and write it down
experiments
“What do you think has to happen to the voltage
(2 or 3
if any bulb is made for less than 110V and the
students)
light set still works?”
4/10
EDSE 732 SECONDARY SCIENCE METHODS
4/17/10
Lesson Plan – Inquiry teach on the application of Ohm’s law
Moritz Huegle
S set up an experiment modeling the series of
light bulbs in the light set
transparency
“How many different circuits can you find in your
or big sheet
set up?”
of paper
S measure current, voltage and resistance
“Is any of these quantities constant or almost
constant according to your data?”
“Think of errors and inaccuracy in your
measurements. Considering these facts can
you assume that any of the quantities is
constant?”
“Try measuring two light bulbs as one
resistance and compare the results to those of
two single light bulbs.”
S draw conclusions about the relationship
between the quantities
“How did we define the resistance R?”
S summarize their data and conclusions on a
transparency or big sheet of paper
10
Presentation
Review
Two groups present their work:
S presenting
-
the hypothesis
OHP or
-
the experiments
poster on the
Summarize
-
the results (comparison with hypothesis)
blackboard
and
-
the schematic circuit diagram
recapitulate
-
relationship between current, voltage
findings and
and resistance
conclusions
15
Review
Test findings on the light set
Class work
“What happens if one light bulb is taken out?”
Light set
“I want to take my light set back to Germany.
Application
Our sockets provide 220V. Do I have to worry?
Blackboard
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EDSE 732 SECONDARY SCIENCE METHODS
4/17/10
Lesson Plan – Inquiry teach on the application of Ohm’s law
Moritz Huegle
5
Stating the
“If any bulb in a series circuit burns out, all the
problem
other turn off! This doesn't happen in our
Impulse
everyday life. If you switch of the light in one
Instructions
room it doesn't necessarily turn off in another
Frontal
for the
room”
introductions
experiments
“Think of another way to arrange the bulbs in a
circuit and measure the current, voltage and
resistance. How do they relate this time?”
20
Laboratory
S come up with a circuit solving the problem
Group
(parallel circuit)
experiments
“Do you maybe need smaller circuits in your
(2 or 3
overall circuit?”
students)
“How many different circuits can you find in your
set up?”
“Check what happens if you take one bulb out
transparency
of the circuit!”
or big sheet
S measure current, voltage and resistance in
of paper
the circuit
“Is any of these quantities constant or almost
constant according to your data?”
“Think of errors and inaccuracy in your
measurements. Considering these facts can
you assume that any of the quantities is
constant?”
“What do you think ‘happens’ to the current at a
vertex in your circuit?”
S draw conclusions about the relationship
between the quantities
“Look at the results of the previous experiment.
What has changed?”
“How could you transform the equation for the
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EDSE 732 SECONDARY SCIENCE METHODS
4/17/10
Lesson Plan – Inquiry teach on the application of Ohm’s law
Moritz Huegle
definition of the resistance knowing that now the
voltage is constant?”
S summarize their data and conclusions on a
transparency or big sheet of paper
10
Presentation
Two groups present their work:
S presenting
-
the circuit
-
the schematic circuit diagram
OHP or
-
the results
poster on the
-
relationship between current, voltage
blackboard
and resistance
5
Review
homework
S recapitulate and summarize their findings
Silent student
about parallel circuits
activity
S finish the task on parallel circuits
Work sheet
and series circuits
S perform calculations in series and parallel
circuits
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EDSE 732 SECONDARY SCIENCE METHODS
4/17/10
Lesson Plan – Inquiry teach on the application of Ohm’s law
Moritz Huegle
8. Assessment
The students will be given a handout about the laboratory sections in advance of the
laboratory. The handout provides them with additional information about what they might
want to focus on.
During the laboratory students will be asked some questions based on what they have
explored and what conclusions they might draw from it. Example questions (written in
italics) are to be found in the laboratory sections in the Instructional Sequence.
In the first review section after the laboratory on series circuits the students will be given
a problem that will be solved together at the blackboard.
The students will also be given a work sheet (see addendum 10.3) at the end of the
lesson. This work sheet is supposed to review the subject of the lesson and the
recapitulate the conclusions.
It also includes some calculations dealing with the applications of the derived
relationship and formulas.
The assignment asks the students to find out more about the physics of a light set.
9. References
National Science Education Standards (1996)
Retrieved August 23, 2009, from The National Academies Press
Web Site: http://www.nap.edu/openbook.php?record_id=4962
South Carolina Curriculum Standards (2005)
Retrieved August 23, 2009, from South Carolina Department of Education
Web Site: http://ed.sc.gov/agency/Standards-and-
Learning/AcademicStandards/old/cso/standards/science/
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EDSE 732 SECONDARY SCIENCE METHODS
4/17/10
Lesson Plan – Inquiry teach on the application of Ohm’s law
Moritz Huegle
10. Addendum
10.1. Handout: Instructions for the experiment on the series circuit
Experiment I
„How does the Christmas light set work?“
1. Think about an explanation how the light set might work and write it down on the
transparency/big sheet of paper
2. Choose from the given material to build a circuit, that is a “small“ light set and
draw the schematic circuit diagram
3. Measure current, voltage and resistance at each light bulb and for the whole
circuit.
Remember:
- Measure the current between the light bulbs and NOT at the light bulb
- Measure the voltage and resistance right at the light bulb, the one wire in front
of the light bulb and the second wire behind it
4. Find the relationship between current, voltage and resistance
5. Summarize your data and conclusions on a transparency or big sheet of paper
10.2. Handout: Instructions for the experiment on the parallel circuit
Experiment II
“How to make sure that the light bulbs don't turn off, if one burns out”
1. Choose from the given material to build a circuit, in which the light bulbs don't
turn off, if one burns out.
2. Draw the schematic circuit diagram
3. Measure current, voltage and resistance at each light bulb and for the whole
circuit
Remember:
- Measure the current between the light bulbs and NOT at the light bulb
- Measure the voltage and resistance right at the light bulb, the one wire in front of the
light bulb and the second wire behind it
4. Find the relationship between current, voltage and resistance
Hint: Pay attention what is constant in this case compared to the first experiment
5. Summarize your data and conclusions on a transparency or big sheet of paper
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EDSE 732 SECONDARY SCIENCE METHODS
4/17/10
Lesson Plan – Inquiry teach on the application of Ohm’s law
Moritz Huegle
10.3. Work sheet: Reviewing the subject and calculation of some problems
Review and problems about series and parallel circuits
1. In a parallel circuit all the light bulbs shine _________________.
2. Missing a bulb in a parallel circuit __________ effect the other bulbs, because
the number of circuits is ______________.
3. The ___________ in a parallel circuit is ___________.
4. Draw a schematic circuit diagram of a parallel circuit with two light bulbs in there.
5. Suppose that in the circuit above one light bulb has a resistance of R1=10Ω and
the other one has a resistance of R2=25Ω. The voltage is U=10V. Calculate the
total resistance Rtotal and the currents at the significant points in the circuit.
6. The light set is a ___________ circuit, because there is _________ circuit and if
one bulb is taken out or burns out all the others _______________.
7. The _____________ in a series circuit is ___________.
8. ______________ and _____________ are added.
9. Draw the schematic circuit diagram of a serious circuit with 4 light bulbs in it and
indicate the resistances, voltages and currents.
10. A Christmas light set includes 20 similar light bulbs. The light set is then plugged
in into a socket with U=110V. Which voltage does every light bulb have to hold
up to?
11. Suppose that in a light bulb one bulb is burnt out and contact is illegally bypassed with tinfoil. What is going to happen to the other light bulbs?
IMPORTANT: Don’t try this at home. It is really dangerous!!!
Bonus problem: If you look at today’s light sets you will find out that they don’t turn off if
one bulb is missing. Find out how this works. (Feel free to browse the internet, look it up
in books,…)
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